1. Field of the Invention
The present invention relates to a DVD (Digital Versatile Disc) video player provided with a play-position function in which, when the power is turned off during playback, the last play position is stored, and then when the power is turned on again, playback can be resumed from the last stored play position.
2. Description of the Related Art
Recently, with the help of the MPEG 2 (Moving Pictures Experts Group) data-compression method, the art for storing video information such as a long movie or TV program on a DVD has been advanced such that a considerable amount of data can be stored on a small disc. DVD video players for playing back this type of DVD have been widely used. Since a DVD can contain long videos, users often have to stop the DVD video player in the middle of playback, and afterwards, resume from where the user last stopped.
Where a CD is used as a conventional small storage medium, CD players are provided with a memory for storing a play position in order to deal with this stopping situation. When the power is turned off during playback, CD players store the last play position in the memory. Thereafter, when the power is turned on again, CD players read the last play position from the memory and thus cause a pickup to move to the last stored play position, so that the CD players resume playing back the CD from where the CD was last stopped.
A memory function for storing the last play position when the power is turned off during playback and then resuming from the last stored play position read from the memory when the power is turned on again, is called a “play-position memory” (PPM) function. In the above-described CD players installed in a vehicle, the CD players are turned on and off due to the on/off operation of the main unit power source of the CD player. In addition, the CD players are sometimes turned on and off, at a part that is closer to the power source of the vehicle, by means of an accessory switch (Acc switch) that is operated by a key. In either case, the CD players can be effectively operated.
An actual circuit construction for realizing the above play-position function is considered as follows. The memory is connected to a system control device for controlling the whole system including each component of the player. Disconnection from the power is detected by, for example, a drop in the power-supply voltage, which activates the system control device. The activation of the system control device, at the time of detecting the voltage drop, causes the play position of the disc being played back to be stored in the memory. Thereafter, when the power is turned on again, the last play-position stored in the memory is read.
However, in a circuit having the above-described construction, when the system control device and mechanisms and other circuits of the player share a power supply, turning off the power supply causes the system control device to be simultaneously disconnected. When the play position is being written into the memory at this time, the voltage applied to a CPU may be lower than the CPU's operational voltage. When this occurs, storage of the current data becomes incomplete. A mixture of current data to be stored and previously stored data may occur, which leads to abnormal data. Particularly in an audio device installed in a vehicle, the power on-off switch of each device connected to the audio device is provided, and the accessory switch is provided as the key switch in a part which is closer to the power supply side. When the user exits the vehicle leaving the audio device turned on, the user will most likely turn off the accessory switch directly without turning off the audio devices and the like. Therefore, the above-described case often occurs.
As a measure for this case, in the CD player, another power system is provided for the CPU that controls the whole player so as to be isolated from the main power system of other mechanisms and circuits. Furthermore, the voltage drop caused by the power-off operation or the like applied to the player and the like is detected by constantly monitoring the power supply voltage across the main power system. When a voltage drop is detected, the last play position is stored in the memory. In an appropriate elapse of time after completion of the storage, the power supplied to the CPU is disconnected. Accordingly, even though the power is abruptly turned off during playback of the CD, the last play position can be successfully stored. Thereafter, when the power is turned on again, playback can be successfully performed from the last play position.
The same consideration is applied to DVD players. Current DVD players adopt a construction in which the power system for the DVD player system control device is shared with the power system for the entirety thereof. Accordingly, when the power-off occurs in the above-described manner, since the operation voltage across the system control device is reduced while the last play position is being written in the memory, storing data in the memory fails. This means that the play-position memory function may not perform appropriately.
To deal with this, by applying the same measure as in the CD player to the DVD player, another power system for the system control device which is isolated from the power system for other mechanisms and circuits is provided, and the power system for the system control device is turned off after all necessary data is stored in the memory.
However, if the control device that performs the above-described play-position function adopted by the CD player was desired to be embedded into the conventional DVD player, the power system design would have to be drastically changed. In addition, this change may affect other control units, thereby requiring a modification of the entire DVD player.